Re: [Hampshire] [OT] memory sticks

2009/3/18 Hugo Mills <hugo@???>:
> On Wed, Mar 18, 2009 at 11:04:53PM +0000, Adrian Bridgett wrote:
>> > Basically, why one might prefer:
>> > CT2KIT12864AA667 • DDR2 PC2-5300 • CL=5 • Unbuffered • NON-ECC • DDR2-667 •
>> > 1.8V • 128Meg x 64
>> > to:
>> > CT2KIT12864AA800 • DDR2 PC2-6400 • CL=6 • Unbuffered • NON-ECC • DDR2-800 •
>> > 1.8V • 128Meg x 64

>> Second one is a tad faster, not that you are likely to notice any
>> difference at all.
>
>   Higher bandwidth, but the same latency -- it takes one more clock
> cycle to find a page on the higher-rated unit, although it works out
> as pretty much exactly the same wall-clock time (7.5ns), because the
> clock rate is faster.
>
>   Hugo.

.... where the 7.5 ns is got from :
the 6 (in CL=6)
times 1.25 ns, and
1.25 * 10^-9 is 1 second
divided by the 800 (from the DDR-800 and also the AA800 phrase).

So for the other stick, latency is
10^9 / 667 = 1.5 MHz, times 5 cycles,
also = 7.5 ns.

And higher bandwidth because once the pipelines are primed the 800MHz
chip pumps the data through at a higher rate.